I found a reference to DTSUSER, which appeared to be from Warehouse Builder. Is it possible that you had that product installed at one point? Rather than delete it the user was renamed just in case someone was actually using it, then it could easily be reinstated.

We do that. When we aren't sure if a user isn't being used and hasn't been logged into in a while we rename it. If nobody complains after a certain amount of time we drop it. Maybe that is what you have.

I certainly wouldn't drop it without confirming that and doing an export of the user just in case.